This invention relates to color cathode ray tubes of the type having a shadow mask, and especially to a system for suspending a shadow mask adjacent to a faceplate portion of the tube. This invention has applicability to suspension systems for shadow masks of various types and to the suspension of shadow masks on tube envelopes of various constructions.
In its preferred execution, the invention of the parent application represents an improvement on the mask suspension system described and claimed in certain of the referent copending applications, particularly U.S. Pat. No. 3,999,098, issued Dec. 21, 1976. In accordance with the invention described and claimed in that application, a plurality of mask suspension devices are provided, each of which comprises a novel sheet metal bracket. The bracket has a pair of arms which are welded on adjoining sides of a mask corner. It is not certain whether such a mask and mask suspension system require thermal "Q" compensation, that is, provision for adjusting the "Q" distance between the mask and faceplate to compensate for thermally induced mask expansion and contraction. However, if such is deemed to be necessary, the aforesaid referent copending application teaches that such can be provided by forming the bracket from a laminate type (side-bonded) bi-metallic material.
It has been found, however, that to provide thermal compensation by the use of a laminate-type bimetallic bracket has a number of shortcomings. First, the cost of laminate bimetallic material is very high, a factor which strongly militates against the use of such a material. Second, it has been found to be quite difficult to weld such a bracket made from a laminate bimetallic material to a shadow mask as described. There are two reasons for this. First, the bracket is of relatively thick material (for example, about 60 mils) compared to the shadow mask (typically about 6 mils). Without more, it will be recognized that some difficulty will be had in attempting to weld a relatively thick bracket to a relatively thin shadow mask.
Secondly, assuming the bimetallic laminate material to be, for example, invar on the side away from the faceplate and stainless steel on the side closest to the faceplate, because the stainless steel has a higher coefficient of expansion than invar (as it must if the mask is to move toward the faceplate when heated), then the stainless steel is on the side of the bracket which must be welded to the shadow mask. But stainless steel has a higher electrical resistance than cold-rolled steel, the material from which a shadow mask is typically made. This means that in order to achieve an adequate weld, an amount of electrical power must be applied during the welding operation which is apt to injure the shadow mask. Specifically, weld currents high enough to achieve satisfactory welding effects on the stainless steel are apt to burn the relatively thin, cold-rolled steel shadow mask.
The result of these welding difficulties is a reduced yield in the attachment of the brackets to the shadow mask. The resulting reduced yield is, of course, translatable into a higher per unit cost of the shadow mask and its suspension system.
The mask suspension systems of the referent copending applications have achieved noteworthy success in developmental tests. This invention, however, represents an improvement over the systems of the said applications in applications where it is desired to provide economies in the manufacture of mounting means for shadow mask assembles.
______________________________________ Other Prior Art ______________________________________ U.S. British ______________________________________ 2,823,328 Vincent 1,278,633 2,922,063 Haas 1,278,632 2,961,560 Fyler 1,278,635 3,497,746 Duistermaat et al 1,772,334 3,529,199 Duistermaat et al Japanese 3,537,159 Gartner 45-32495 3,548,235 Duiedijk et al German 3,573,527 Hofkenscheid et al OLS 2454 415 OLS 2454 416 ______________________________________